Catalytic Dehalogenatin of Perchloroethylene in a Redox Environment

Persistent Link:
http://hdl.handle.net/10150/194238
Title:
Catalytic Dehalogenatin of Perchloroethylene in a Redox Environment
Author:
Orbay, Ozer
Issue Date:
2005
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
The catalytic dehalogenation of tetrachloroethylene (PCE) occurs via oxidation or reductive hydrodechlorination. Catalytic oxidation uses oxygen to dehalogenate PCE into CO₂ and Cl₂. This process requires higher temperatures >350°C then reductive hydrodechlorination and can produce undesirable toxic products, such as dioxins and furans. Hydrodechlorination uses a reductant to reduce PCE to ethane, and intermediate products such as less chlorinated hydrocarbons. Catalyst deactivation and associated loss of activity are commonly observed. Here, we examined a redox environment for the destruction of PCE on commercially available and laboratory made precious metal loaded catalysts. When a mixture of PCE, oxygen and hydrogen are passed over the catalyst, the PCE is converted to ethane, CO₂, water, and HCl as a function of temperature (ambient to 450°C) and hydrogen to oxygen ratio in the feed (0 to 5). In the laboratory experiments, high conversion of PCE was observed for relatively high H₂/O₂ ratios (84% conversion with H₂/O₂ = 2.15, 63% with H₂/O₂ = 1.18 at 350°C, for commercial catalyst) for retention time of ~ 1 s. The conversion of PCE generally increased with increasing temperature for all H₂/O₂ ratios. In the strictly oxidation environment (H₂/O₂ = 0), PCE conversion was lower than with hydrogen at any given temperature (<30% at 464°C). At lower temperature (<350°C) the dominant carbon-containing product was ethane, under redox conditions. At high temperature (>380°C) CO₂ eluted from the reactor, suggesting that oxidation of reduction products or PCE occurs. Experiments were conducted by using a laboratory made catalyst. A mixture of three types of precious metals (Pt, Pd, and Rh) was impregnated onto a monolithic alumina support. These studies show no apparent performance difference between the two catalysts at high temperatures (>280°C). However, at low temperatures the laboratory catalyst outperforms the commercial catalyst. It was speculated that this difference due to high metal loading of the laboratory catalyst (38.61 mg versus 1.27 mg). A field scale study of the commercial catalyst was undertaken at the Superfund Park-Euclid site in Tucson, Arizona, where the soil is contaminated with PCE and other volatile hydrocarbons. Gases from a soil-vapor extraction unit were fed to the reactor, Even though the soil vapor contained high oxygen (>17%), high PCE conversion with and without hydrogen was observed. Due to the relatively high cost associated with the use of hydrogen, propane, methane, and diesel were investigated as replacement reductants. The results indicate that propane and diesel are promising replacements for hydrogen that deserve further investigation.
Type:
text; Electronic Dissertation
Keywords:
Environmental Engineering
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Environmental Engineering; Graduate College
Degree Grantor:
University of Arizona
Advisor:
Arnold, Robert G.
Committee Chair:
Arnold, Robert G.

Full metadata record

DC FieldValue Language
dc.language.isoenen_US
dc.titleCatalytic Dehalogenatin of Perchloroethylene in a Redox Environmenten_US
dc.creatorOrbay, Ozeren_US
dc.contributor.authorOrbay, Ozeren_US
dc.date.issued2005en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractThe catalytic dehalogenation of tetrachloroethylene (PCE) occurs via oxidation or reductive hydrodechlorination. Catalytic oxidation uses oxygen to dehalogenate PCE into CO₂ and Cl₂. This process requires higher temperatures >350°C then reductive hydrodechlorination and can produce undesirable toxic products, such as dioxins and furans. Hydrodechlorination uses a reductant to reduce PCE to ethane, and intermediate products such as less chlorinated hydrocarbons. Catalyst deactivation and associated loss of activity are commonly observed. Here, we examined a redox environment for the destruction of PCE on commercially available and laboratory made precious metal loaded catalysts. When a mixture of PCE, oxygen and hydrogen are passed over the catalyst, the PCE is converted to ethane, CO₂, water, and HCl as a function of temperature (ambient to 450°C) and hydrogen to oxygen ratio in the feed (0 to 5). In the laboratory experiments, high conversion of PCE was observed for relatively high H₂/O₂ ratios (84% conversion with H₂/O₂ = 2.15, 63% with H₂/O₂ = 1.18 at 350°C, for commercial catalyst) for retention time of ~ 1 s. The conversion of PCE generally increased with increasing temperature for all H₂/O₂ ratios. In the strictly oxidation environment (H₂/O₂ = 0), PCE conversion was lower than with hydrogen at any given temperature (<30% at 464°C). At lower temperature (<350°C) the dominant carbon-containing product was ethane, under redox conditions. At high temperature (>380°C) CO₂ eluted from the reactor, suggesting that oxidation of reduction products or PCE occurs. Experiments were conducted by using a laboratory made catalyst. A mixture of three types of precious metals (Pt, Pd, and Rh) was impregnated onto a monolithic alumina support. These studies show no apparent performance difference between the two catalysts at high temperatures (>280°C). However, at low temperatures the laboratory catalyst outperforms the commercial catalyst. It was speculated that this difference due to high metal loading of the laboratory catalyst (38.61 mg versus 1.27 mg). A field scale study of the commercial catalyst was undertaken at the Superfund Park-Euclid site in Tucson, Arizona, where the soil is contaminated with PCE and other volatile hydrocarbons. Gases from a soil-vapor extraction unit were fed to the reactor, Even though the soil vapor contained high oxygen (>17%), high PCE conversion with and without hydrogen was observed. Due to the relatively high cost associated with the use of hydrogen, propane, methane, and diesel were investigated as replacement reductants. The results indicate that propane and diesel are promising replacements for hydrogen that deserve further investigation.en_US
dc.typetexten_US
dc.typeElectronic Dissertationen_US
dc.subjectEnvironmental Engineeringen_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineEnvironmental Engineeringen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorArnold, Robert G.en_US
dc.contributor.chairArnold, Robert G.en_US
dc.contributor.committeememberSaez, A. Eduardoen_US
dc.contributor.committeememberBetterton, Eric A.en_US
dc.identifier.proquest1423en_US
dc.identifier.oclc137355580en_US
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